This invention generally relates to a no break power transfer system. More particularly, this invention relates to ensuring that there is an appropriate frequency match when transferring power between different supplies in a no break power transfer system.
There are various known arrangements where a secondary or back-up power supply is used in the event of a main power supply failure. There are other situations where auxiliary or back-up power supplies are strategically used on a temporary basis even though the main power supply may be completely functional.
One example situation where multiple power supplies are utilized is on a modern aircraft. There typically is a main power supply that is sometimes referred to as a main engine generator. An auxiliary power unit (APU) is used in place of the main power supply for various reasons known in the art.
For a successful switch between power supplies without interrupting power to the electrical component, a so-called no break power transfer is required. This typically involves simultaneously coupling both power supplies to the load and then disconnecting a selected one of the power supplies. The output of the power supplies typically matches so there is no problem when they are both coupled with the load and there is no discernable break in power at the load.
Traditionally, the auxiliary power unit and the main power supply were set to meet appropriate needs of the aircraft electrical systems. More recently, however, it has been increasingly proposed to use variable frequency alternating current electrical bus networks in place of traditional constant frequency systems. The variable frequencies that may be used introduce further complexities to achieve a successful no break power transfer. This invention addresses the need for ensuring that an appropriate frequency match occurs during a no break power transfer.
In general terms, this invention is a no break power transfer system that ensures that there is an appropriate frequency match associated with the outputs of multiple power supplies during a no break power transfer.
One system designed according to this invention includes a main power supply that is selectively coupled to a load. An auxiliary power unit is selectively coupled to the load. A frequency adjuster is between the auxiliary power unit and the load for selectively controlling the frequency of the power available from the load from the auxiliary power unit. The frequency adjuster ensures that there is a frequency match between the alternate supplies to the load during a no break power transfer.
In one example, the frequency adjuster includes a controller that monitors the frequencies on the supply lines to the load associated with the different power supplies. The controller operates an inverter that controls the frequency of the power available from the auxiliary power unit.
In one example, the inverter modifies the frequency of the power received from the auxiliary power unit as needed when the power transfer is made in either direction between the main power supply and the auxiliary power unit.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawing that accompanies the detailed description can be briefly described as follows.